Asphalt permeability measurement apparatus



May 25, 1965 w. H. ELLIS ETAL ASPHALT PERMEABILITY MEASUREMENT APPARATUSFiled June 28, 1961 4 Sheets-Sheet l INVENTORS WILL/AM H. ELLIS JSCHMIDT May 25, 1965 w. H. ELLIS ETAL ASPHALT PERMEABILITY MEASUREMENTAPPARATUS Filed June 28, 1961 4 Sheets-Sheet 2 FIG. 2

WILL/AM H. ELLIS ROBERT J. SCHMIDT y 1965 w. H. ELLIS ETAL 3,184,957

ASPHALT PERMEABILITY MEASUREMENT APPARATUS Filed June 28. 1961 4Sheets-Sheet 3 20 30 4o 50 PERMEABILITIES OF PAVEMENTS IN PLACE(MLjMlN/lNCH FIG 4 CORRELATION OF PERMEABILITIES OF PAVEMENTS IN PLACEWITH PERMEABILITIES OF PAVEMENT CORES INVENTORS WILLIAM H ELL/5 ROBERTJ. SCHMIDT y 1965 w. H. ELLIS ETAL 3,184,957

ASPHALT PERMEABILITY MEASUREMENT APPARATUS Filed June 28. 1961 4Sheets-Sheet 4 WILLIAM H. ELL/S ROBERT J. SCHMIDT United States Patent:William H. Ellis, El Segundo, and Robert J. Schmidt, El

Cerrito, Calif., assignors to California Research Corporatlon, SanFrancisco, Calif., 21 corporation of Delaware Filed June 28, 1961, Ser.No. 120,358 2 Claims. (Cl. 73-38) The present invention relates to amethod of determining permeability, in situ, of construction materialssuch as concrete without requiring removal of samples, as

by coring and the like. More particularly, this invention is directed toa method and apparatus for measuring the vapor permeability of materialssuch as asphalt concrete by isolating a limited area of the finished andundisturbed surface from the atmosphere and flowing air therethrough tomeasure its permeability in situ.

It is a particular object of the present invention to provide a methodand apparatus for measuring in place the degree of compaction of anasphalt concrete, so that such material may be rolled or tamped to adesired degree while it is still sufficiently plastic to permit furtherworking. By such in-place measurements, for example, it is possible tocontrol compaction to a degree where the asphalt concrete issubstantially water impervious, but still vapor pervious.

In carrying out the method of the invention, a limited area of thesurface of the material, such as asphalt concrete, is isolated under avapor space formed preferably by a fluid chamber that is scalable to thesurface of the material. A pressure differential, sufficient to create aflow of air through the material, is then established between atmosphereand the vapor space. Desirably, this pressure differential is measuredby a gauge connected to the vapor chamber. The rate of flow of air atthe set pressure differential is then measured over a period of timesufficient to establish equilibrium flow conditions for fluid flowthrough the isolated area. In a preferred form of apparatus, suchpressure differential is created by an enclosed liquid reservoir systemhaving a vapor space connected to the vapor chamber, so that measuredamounts of liquid moving into or out of the reservoir may be timed. Thevapor space in the reservoir system is accordingly altered to create thedesired pressure differential between atmosphere and the fluid chambersealed to the surface of the concrete. The rate of fluid movement in thereservoir system will thus be a measure of the rate of flow of vaporthrough the cement. This measurement is directly correlatable topermeability of the material.

There has long been a need for a method of determining the degree ofcompaction of asphalt concrete while it is still in its plasticcondition, so that it can be rolled or tamped to a proper degree withoutwaste of time and materials. Heretofore, it has been the practice tocompact such asphalt concrete to a degree that is determined by itssurface appearance. Such a procedure is an art that depends upon thesupervisors experience rather than upon a defined method of measuringdegree of compac tion. It is known that the useful life of asphaltpavements may be increased by limiting the rate of transfer of oxygen,Water, and microorganisms from the surface to the interior of thematerial, and the escape of volatile constituents from the interior tothe surface. This transfer of material into and out of asphalt concretecan be minimized by properly compacting for minimum permeability. Toreach such a minimum, it is necessary to have a method of optimizing theamount of compaction applied to the material.

84,957 Patented May 25, 1965 "ice Heretofore, it has been common todetermine the percent of theoretical compaction of the material after ithas cooled and hardened. This is done by taking a sample of the rawmaterial and compacting it into a core with a known force. A sample ofthe hardened material is then cut as a core from the finished concrete.The ratio of the density of the second core to the first is expressed asa percent of theoretical compaction. This value is in fact only ameasure of the air voids in the finished concrete, and not a measure ofits permeability to fluid flow. Obviously, such a procedure is notsuitable for determining the degree of compaction while the mixture isstill hot and can be further rolled or compacted to achieve optimumpermeability of the finished material.

While the present apparatus is described as being useful for theperformance of a method of measuring permeability, and degree ofcompaction of asphalt concrete in situ, it will also be apparent thatthe permeability measuring equipment may be used for measuring, in situ,other large horizontal or vertical surfaces whose permeability is ofimportance, under undisturbed conditions and without requiring removalof samples or plugs. Other materials to which the apparatus can beapplied for such measurements are Portland-cement concrete, or materialstreated with impregnating fluids, such as timber used for telephonepoles, railroad ties, and the like.

Further objects and advantages of the present invention will becomeapparent from the following detailed description taken in conjunctionwith the accompanying drawings.

In the drawings:

FIG. 1 is a schematic representation of a permeability apparatusconstructed in accordance with the present invention and adapted toperform the method.

FIG. 2 is an alternative arrangement of the apparatus, arranged to applyvacuum across the pressure measuring chamber.

FIG. 3 is a schematic representation of the apparatus of FIG. 1 in useas a permeability measuring device for cores, and a core adaptertherefor.

FIG. 4 is a graph showing the correlation of permeabilities of pavementsin situ, as measured with the arrangements shown in FIGS. 1 and 2, withthe permeability of pavement cores, as measured by the apparatus shownin FIG. 3.

FIG. 5 illustrates a preferred construction of a rapid ring-sealerarrangement for a permeability measuring chamber.

Referring now to the drawings and in particular to FIG. 1, there isillustrated a preferred form of apparatus for carrying out the method ofthe present invention. As

'there shown, a limited area of the surface of the con crete is isolatedin place and without removing a sample under a vapor space, formed bydome 12. Rim 13 of dome 12 is sealed by grease 14 or other readilyadherent materials, so that the compacted surface of the concrete isenclosed under this fluid chamber. A predeterminable pressuredifferential between atmosphere and the space under dome 12 is createdby the liquid reservoir arrangement comprising sump chamber and flowmeasuring chambers 17 and 19. As indicated in the drawings, all of thereservoir chambers 15, 17, and 19 are desirably constructed oftranslucent materials, such as glass, but it is possible to make them ofopaque materials, such as metal, if sight level gauges are incorporatedwith the apparatus.

As will be apparent from the arrangement in FIG. 1, a pressure gauge,represented by manometer 21, is interconnected to vapor chamber, ordome, 12 by conduit 23.

Desirably, manometer 21 is mounted adjacent the pair of liquid meteringreservoirs 17 and 19, so that a predeterminable pressure differentialcan be established within the 3,18&,957

; fluid flows out of metering chambers 17 and 19 controlled respectivelyby valves 27 and 29, the in-place permeability of pavement may bemeasured in units of milliliters per minute persquare inch. The singleunknown to be measured under these conditions is the time required for afixed volume of liquid to flow from the metering chambers 17 and 19 intothe sump reservoir 15. Time is most conveniently measured by an operatorwith a stop watch.

To initiate operation of the apparatus, liquid such as water in sump israised into one, or both, of the sample measuring reservoirs 17 and 19by the application of air pressure to vapor space at the top of sump 15.In FIG. 1, this air pressure supply is indicated as a gas sampling bulb32. Bulb 32 is, in effect, a rubber bladder with suitable check valvesat its intake end 33 and its output end 34. Pressure exerted by bulb 32is applied through suitable ports in three-way control valve 36, whichinter+ connects the bulb with tube 37, which in turn communicates withvapor space 30. At the same time, valve 36 shuts off communication tovapor dome 12 by Way of tube 39".

' Valves 27 and/ or 29 are then opened so that water in sump 15 can bepumped upwardly into measuring reservoirs 17 and 19. When a desiredvolume of liquid is trapped in the reservoirs 17 or 19, valves 27 or 29are again closed and three-way valve 36 turned to the position indicatedin FIG. 1. In this position, vapor space 30 in sump 15 communicates withvapor dome 12 through tubes 37 and 33. Then one of the valves, 27 or 29,say 27, is opened sufficiently to permit Water to flow out of reservoir17 to raise the level in sump 15. This flow forces air, or vapor,

out of space 30 into dome 12 and thence downwardly through a volume ofconcrete 10 enclosed by seal 14 around rim 13. The pressure at which airflows through this volume of concrete 10 is indicated by manometer 21.Obviously, the air flow rate will be dependent upon the permeability ofthe concrete and the pressure differential established by the flow ofliquid from reservoir 17 into sump 15. The liquid flow can be adjustedso that the pressure differential is at a desired value, say .15 inch,as indicated in the example in FIG. 1. The time required for a knownvolume of liquid to flow is then measured. I

Preferably, an operator measures the time required to displacemilliliters by noting the change in level between the SO-millilitermarks 18 on reservoir 17. This time-and-volume measurement to detectrate may be made automatically with a photoelectric cell and lightsource. Light from the source may either transmit through the liquid orreflect from the surface to one or more photocells set to detectmovement of liquid between selected reference levels on reservoir 17.The rate is then recorded against time on a chart or strip recorder.

Where the permeability of vapor in concrete 10 is considerably higherthan can reasonably be measured by flow of water from measuringreservoir 17, it is preferable to measure liquid flow with measuringreservoir 19. The two spherical volumes 25 and 26-are desirably oneliter volume each, to give a total volume of two liters (2,000

'39 provide necessary air pressure and flow connections to vapor dome12, which is then mounted in a suitable 'lomaterial.

42 cation on the surface of the asphalt'concrete then being compacted.Desirably, several measurements are made in succession at selectedlocations on the surface to obtain a statistically reliable value.

Referring now to the arrangement shown in FIG. 2, it will be noted that,as compared to FIG. 1, tube 39 has been moved to port 45 and controlvalve 41, and tube 37 can be vented .to atmosphere by three-wayvalve 36and port 38. Additionally, conduit 23 has been moved frompressure-measuring tap 24 on manometer21 to vacuummeasuring tap 22. Itwill be. seen that, with this arrangement, a slight vacuum can beapplied to the limited area below vapor dome 12 by releasing fluid inmeasuring reservoir 17 for return into sump 15. Thus, the pressuredifferential applied across the limited volume of the in-situ sample ofconcrete 10 may be either vacuum, as in FIG. 2, or pressure, as in FIG.1.

FIG. 3 illustrates apparatus for measuring the vapor permeability of acylindrical core taken from a building material, such as asphaltconcrete, with the same form of apparatus illustrated in FIGS. 1 and 2.However, in the apparatus of FIG. 3, vapor dome 12A has been modifled byremoving rim 13 (FIG. 1), so that .the cylindrical portion 11 of dome12A is substantially continuous with the diameter of the pavement core10A. Glass dome 12A is then sealed to core 10A by a rubber sleeve 50which has an internal diameter only slightly larger than core 10A andthe cylindrical wall 11, so that the latter may be easily inserted intosleeve 50. Ends 51 and 52 of sleeve 50 are then turned back over theends of a cylinder 54 constructed of glass or the like. The outerdiameter of rubber sleeve. 50 is smaller than the inner diameter ofcylinder 54, so that the unit comprising core 10A, dome 12A, and sleeve50 easily inserts into cylinder 54 and leaves an annular spacetherebetween. In this way, an air pressure seal is formed by connectingan air pump, such as gas sampling bulb 55,'to the annular space throughconduit 57 and three-way valve 59. By reducing the pressure in theannular space, sleeve 50 shrinks around core 10A and dome 12A. This coreadapter can then be'used to measure the permeability of a standardpavement core using either the pressure-applying apparatus of FIG. 1 orthe vacuum apparatus of FIG. 2.

We have found that permeabilitymeasurements made by the present methodcorrelate closely with values obtained with cores cut from the completedconcrete. In particular, it is surprising that the vertical permeabilityof a relatively small area, such as that enclosed by dome 12 or 12A, isnot greatly affected by the horizontal permeability of the concrete.FIG. 4 shows this relationship. It is a graph of permeabilities ofasphalt pavements measured in place versus the vertical, or transverse,permeabilities of pavement cores taken from the same Thesepermeabilities were measured in milliliters per minute per square inch,with the apparatus of FIGS. 1 and 2. By use of this correlation, thevalues measured on the cores, or in place, may be converted to unitsreadily understood in construction of asphalt concrete.

FIG. 5 is a vertical view, partially in cross section, of

apparatus for rapidly isolating a desired area of concrete.

strip off aftereach test. In the FIG. 5 apparatus, the vapor dome,indicated generally 'as 60, includes a cup portion 61 adapted to bevapor-sealed to the vapor-perrr 1 eable surface of concrete 10 by asealant, such as grease 14. The sealant is confined within annular space62 by a pair of O-rings 63and 64 mounted in grooves 65 and 66,

respectively, in the bottom lip or sealing face 67 of unit 60. Grease 14isextruded in a ring through an annular screen member 69 by grease gun70 of conventional design. As

shown, gun 7 may be secured to a boss 72 formed in the center of cup 60.Alternatively, a pressure-type grease fitting may be used. As isconventional in such grease guns, piston member 73 is spring-loaded, asby coil spring 75, so that when retracted by handle '77 to fill chamber78, spring 75 is compressed. Handle 79 includes a ratchet arrangementthat co-operates with notches so on shaft 81 so that each action ofhandle 79 permits piston 73 to be driven downwardly a distance of onenotchspace. Grease from barrel 78 enters port 82 in boss '72 and thendistributes'radially through a plurality of radial bores 84 in theclosed end of cup 69. Each of the radial bores 84 communicates withgrease-dispensing screen 69 through a similar plurality of longitudinalbores 85 intersecting passages 84. The purpose of screen 69 is to limitthe volume of grease left on the surface after the permeability test.This reduces the clean-up time after a test.

In applying the field sealer unit, a suificient volume of grease,plastic, or other viscous material is pumped outwardly through annularscreen 69 so that the space 62. be-

tween 0 rings 63 and 64 will be just filled. Seal face 67 is thenpressed down onto the surface of concrete 10. On a hot surface, it issometimes desirable to weight dome 60, as by manually pressing down onthe top. Two passageways 86 communicate with the ,vapor space formed bythe cup portion, or sealing chamber, 61. Taps 86 are connected to apressure gauge and an air pressure supply chamber, as inthe embodimentsof FIG. 1 or 2.

In the foregoing embodiments, air is used as the fluid for measuringpermeability of the sampled volume. It

' will be apparent that the air will contain .water vapor in an amountdependent upon the temperature of the reservoir system. Other gases canbe used in place of air, such as carbon dioxide, helium, nitrogen, andthe like. In place of water as the vapor-displacing liquid, otherliquids, such as alcohol, mercury, and the like can be substituted.Additionally, liquid permeabilities can be measured with the apparatusdisclosed in FIG. '1, if such characteristic is desired or needed for aparticular application.

While only a few embodiments of the present invention have beenillustrated and described, various modifications in the apparatus may bemade without departing from the method or the inventive concept asexpressed in the appended claims.

We claim: 7

1. For use in an asphalt concrete permeability tester wherein a givenair pressure diiferential is applied to a limited area of said concreteand the air flow rate is measured, a cup member including a flangedmember around the rim of its open end, said flanged member including apair of annular sealing gaskets to define an annular space for retentionof a sealing material therebetween, passageways formed in the bodyportion of said cup member connecting with said annular space betweensaid gaskets, means for supplying sealing material to said passagewaysand a pair of air ports formed in said cup member, said ports includingpipe nipples connectable thereto for attachment of flexible hoses tosaid per- Ineability measuring tester.

2. Apparatus for measuring the permeasibilty of asphalt concrete in situand without requiring removal of samples therefrom which comprises a cupmember vapor chamber having a rim sealable'to a smoothed surface of theconcrete and a pair of ports formed in said cup member, a portablehousing adapted to be positioned in the vicinity of said vapor chamber,a liquid reservoir chamber mounted at the bottom of said housing, a pairof calibrated liquid measuring chambers mounted above said reservoirchamber and interconnected thereto by separate liquid conduits, valvemeans in each of said conduits for controlling flow of liquid betweensaid reservoir chamber and each of said calibrated measuring chambers,one of said calibrated chambers being of substantially greater volumethan the other of said-calibrated chambers, a common vapor conduitconnected to the upper ends of said calibrated chambers and valve meansfor regulating the flow of vapor into and out of said calibratedchambers, another vapor conduit connected to the top of said reservoirchamber, valve means in said other vapor conduit for selectivelycontrolling vapor flow into and out of said reservoir chamber, air pumpmeans connectable through said last-named valve means for selectivelytransferring liquid from said res ervoir chamber to at least one of saidcalibrated chambers, a flow manometer positioned in said housing,flexible tube means for connecting said flow manometer to one of saidports of said cup member, and a second flexible tube for connecting tothe inlet end of one of said vapor conduits whereby vapor will flowthrough the volume of asphalt concrete under said cup member in responseto the transfer of liquid from one of said calibrated measuring chambersat a flow rate controllable bythe opening of one of said valves in oneof said liquid conduits to return liquid from the selected one of saidcalibrated chambers back to said reservoir chamber at a pressure headmeasurable by said manometer.

References (Cited by the Examiner UNITED STATES PATENTS 2,021,948 11/35Schopper 7338 2,949,766 8/60 Kirkham et a1. 7338 FOREIGN PATENTS 534,14812/54 Belgium. 224,011 7/ 10 Germany.

ISAAC LISANN, Primary Examiner.

1. FOR USE IN AN ASPHALT CONCRETE PERMEABILITY TESTER WHEREIN A GIVENAIR PRESSURE DIFFERENTIAL IS APPLIED TO A LIMITED AREA OF SAID CONCRETEAND THE AIR FLOW RATE IS MEASURED, A CUP MEMBER INCLUDING A FLANGEDMEMBER AROUND THE RIM OF ITS OPEN END, SAID FLANGED MEMBER INCLUDING APAIR OF ANNULAR SEALING GASKETS TO DEFINE AN ANNULAR SPACE FOR RETENTIONOF A SEALING MATERIAL THEREBETWEEN, PASSAGEWAYS FORMED IN THE BODYPORTION OF SAID CUP MEMBER CONNECTING WITH SAID ANNULAR SPACE BETWEENSAID GASKETS, MEANS FOR SUPPLYING SEALING MATERIAL TO SAID PASSAGEWAYSAND A PAIR OF AIR PORTS FORMED IN SAID CUP MEMBER, SAID PORTS INCLUDINGPIPE NIPPLES CONNECTABLE THERETO FOR ATTACHMENT OF FLEXIBLE HOSES TOSAID PERMEABILITY MEASURING TESTER.